Previously, as the electrically erasable programmable nonvolatile memory, a flash memory has been well-known, which comprises a memory cell array of NAND-type or NOR-type memory cells each having a floating gate structure. In addition, as the nonvolatile and fast random access memory, a ferroelectric memory has also been known.
On the other hand, as the technologies for much finer fabrication of memory cells, variable resistance memories have been proposed, which use variable resistance elements in memory cells. Known examples of such the variable resistance elements include a phase-change memory element that can change the resistance in accordance with the state change due to the crystalline/amorphous phase of a chalcogenide compound; an MRAM element that uses the resistance variation due to the tunnel magneto-resistance effect; a polymer ferroelectric RAM (PFRAM) memory element of which resistance element is formed of a conductive polymer; and a ReRAM element that can cause a resistance variation in accordance with the supply of an electric pulse.
In the case of, for example, a memory cell that uses the ReRAM element, however, no resistance variation may be caused only when the electric pulse is simply supplied due to the instability of the memory cell. In addition, a resistance variation in a direction opposite to the intended one may be caused. If such the resistance variation in the opposite direction is left, bad influences are concerned, including the shortened life of the memory cell.